1. Field of the Invention
This disclosure generally relates to stringed weapons used for propelling a shafted projectile such as an arrow or bolt.
2. Description of the Related Art
The bow and arrow is a weapon of ancient providence and a relatively simple structure that has not dramatically changed in thousands of years. Conventional and historical bows use a bendable structure connected via a string that has an ability to store the potential energy of a deformation of its longitudinal shape and transfer that to a projectile via a string. The deformation is accomplished by the force of the user's draw on a string attached to two or more support points of the structure of the bow. The bow acts as a flat spring storing the kinetic energy of the draw. The string and bow shape can provide for some mechanical advantage, allowing the structure of the bow to be bent more easily as the force is generally applied at an angle to the bend.
The more the bow is bent, the more stored potential energy is available. However, in traditional bows, the amount of force needed to incrementally increase the draw distance increases as the bow is drawn. Thus, a traditional bow gains much of its power from the last few inches of its deformation. Once the bow has been sufficiently deformed (drawn), a projectile which was previously placed on the string (nocked) is aimed. The string is then suddenly released by the user. The release of the string allows the bow to quickly return toward its non-deformed position converting the potential energy of the flat spring of the bow into kinetic energy in the movement of the string and associated projectile. Once the bow has reached its original (pre-drawn) position or equilibrium point, the string will generally stop suddenly allowing the projectile to leave the string while maintaining its momentum and be fired by the bow.
While there are a number of different variations of this basic system, they all generally utilize the same method of projectile delivery and a huge number of different stringed weapons all utilize this same basic principle of operation. Bows, crossbows, stone-bows, ballistae, and arbalests all utilize the returning force from the deformation of a flat spring to accelerate the string and the associated projectile. In all of them, a flat spring (such as a bent piece of wood or plastic) serves to form the structure of the “bow” and the spring is increasingly bent as the bow is drawn. Generally, the only difference between these stringed weapons are their size, the method of release of the string (such as by a trigger or by hand), the type of projectile that they fire (such as an arrow or bolt), and the method that is used to draw them (whether by hand or utilizing a machine such as a pulley).
While the general concept of the bow as a stringed weapon has not changed for centuries, there have been a number of modern improvements. The most traditional designs of a bow (often referred to as simple or composite bows based on the materials of their construction) generally use a flat or slightly curved piece of material to be the spring. Some other designs, such as recurve, reflex, decurve, and deflex bows all generally utilize the same basic construction, but alter the shape of the spring and utilize curves of a variety of different shapes to improve ease of draw and provide various other benefits. Further, some of these utilize a single flat spring applying load to both ends simultaneously, while others utilize two springs mounted to a more rigid center grip where each flat spring is simultaneously loaded in a cantilever fashion.
A modern compound bow is probably the most technically complex form of bow. A compound bow utilizes a series of pulleys as part of its structure to generally assist in drawing the string and bending the flat springs. This allows for a much more powerful bow to be drawn (and held drawn) more easily. However, even a compound bow generally still utilizes flat springs to ultimately provide the projectile with energy. The springs, however, are generally much more rigid, are often held at specific angles relative to the user and commonly only take up a portion of the bow with most of the bow structure being given over to grips and stabilizing components. This more compact design combined with higher draw strength has made compact bows a common choice for hunters.
The energy storage method of the bow places limitations on the size and weight of the system. As each end of the string is attached to a separate support (specifically, to each end of the bow), the spring is generally bent about the middle where the hand is placed. Thus, more powerful bows often have to utilize a much longer body to make it possible for a user to be able to draw the bow by hand.
On a compound bow, and some more modern bows, the bow actually comprises a pair of cantilever springs each of which is affixed on either side of the handle where the user grips the bow. The string is then connected between them. The use of multiple flat springs (or even a single spring where the exact center is not known) can result in a release of force with a variation between each discrete structure and, thus, these bows have to be carefully balanced and manufactured to produce an accurate firing profile.
While these bow styles are all generally adequate for projecting an arrow in a controlled or competitive environment, use in the wild can generally put a limit on the effectiveness of a bow. Heavy brush can compromise the trajectory and space needed to both accommodate a bow of sufficient draw strength to bring down a large animal and to perform the draw and release cycles of the shooter. Bows are generally quite large devices because of the use of the structure to act as the leaf spring and for the mass of the structure itself to absorb some of the energy of firing. Further, the bows generally need to be held either horizontally or vertically to provide for accurate aiming and to inhibit the bow's retraction from pulling the aim off.
Because of their size, bows (particularly more powerful versions) are not readily transportable. As such, they are often not useable in scenarios where they otherwise may be. For example, a bow is generally much quieter than a firearm making it useful in certain military and hunting tasks. Further, a bow is not a common survival preparation weapon as while it can use much more readily available ammunition, it can be difficult to store and transport compactly.
Additionally, the complexity of modern compound bows inhibits the ability of the user to adjust the draw weight of the string in the field. Generally for a more standard bow, the only adjustment that can be made to firing strength is to “partially draw” the bow, but this is an inexact science and can also readily serve to spoil the aiming. While a compound bow can generally be provided with different draw strengths by altering the specific rotation of the pulleys (which are often asymmetric), special equipment is often needed to perform this task and it often has to be done with the string removed. Thus, changing the draw strength in the field is next to impossible.
Another problem with bows is the inherent danger from structural failure inherent, particularly in compound bows, when the weapon undergoes a dry fire or dry loosing. This occurs when the weapon is fired without a projectile and while archers will avoid doing it, arrows will occasionally become unnocked during the draw, or the target can move making a shot impossible and slowly releasing the draw can be difficult. Dry firing or loosing can be extremely dangerous with a stringed weapon as the projectile of a stringed weapon is generally designed to absorb a large amount of the released energy of the weapon. Without a projectile to absorb the energy, the energy can be dissipated into the structure of the bow and/or string, potentially destroying it structurally and often in an explosive fashion.